Art of cracking hydrocarbons



Filed April l2 INVENTOR Edward )fh/'IMM BY EQ,

m Y a, NN m. s.

ArToRNE Patented Apr. 19, 1932 UNITED STATES PATENT OFFICE YORK, ASSIGNOR T SINCLAIR REFINING Y., A CORPORATION OF MAINE ART OF CRACKING HYDROCARBONS Applicationplnea Aprn 12 This invention relates to improvements in the manufacture of lower boiling hydrocarbon oils, such as gasoline, from higher boiling hydrocarbon oils, such as gas oil, by pressure distillation cracking operations.

Pressure distillation operations have, in the past, been carried out both as batch operations and as continuous operations, the operation being made continuous by the supply of l0 raw stock and the discharge or" residual stock during operation. The batch operation, without the discharge of residual stock during the operation, makes possible a higher yield of loWer boiling products than the con- 15 tinuous operation, that is the batch operationl makes possible the recovery of a larger proportion of lower boiling oil from a given quantity of higher boiling oil. On the other hand, the continuous operation makes possible a longer period of uninterrupted operation and consequently makes possible the cracking of a larger amount of raw stock in a given apparatus over a given period of time, making possible in many cases the production of a larger amount of lower boiling products in a given period of time although this larger amount may represent a smaller proportion of the raw'stock. As will be apparent, the merits of the two types of operation are determined, at least in part, by the economic conditions prevailing at the time.

The present invention provides an improved methd ofroperation which, within limits, combines the advantages of both meth ods of operation, aHording higher yields as compared to continuous operations and afording prolonged periods of uninterrupted operation as compared to batch operations.

The products of pressure distillation cracking operations include, in addition to the desired-lower boiling hydrocarbon oils,

pitchylconstituents which, under some conditions, undergo further decomposition forming coke or coke-likeconstituents.y The j deposit of pitchy or cokey constituents upon heating surfaces through which heat is -transferred to the oil in pressure .distillation cracking operations is one of the major diiiiculties involved -in such operations. Such 59 dihculties may be-controlled as described,for

, 1929. Serial N0- 354,448.

example, in Letters Patent No. 1,598,136 issued to the Sinclair Refining Compan August 31, 1926, on the application of ugene C. Herthel, but this method of operation, as

. any other method of operation involving the discharge of oil components of the charge of oil undergoing cracking, involves a lowering of the yield of lower boiling products. Dificulties due to deposition of pitchy or cokey constituents produced by the cracking operation are increased Where, for example, finely divided absorbent agents or finely divided desulphurizing agents are added to the charge of oil to secure someother benefit.

The present invention provides for concentration Within the pressure distillati-on system of pitchy or cokey constituents produced by the cracking operation, and of any added solids or semi-solids or the reaction products of such additions, and for the separation from such concentrated objectionable constituents, but within the system, of a maximum of those oil components associated therewith.

In carrying. out the present invention, a charge of high boiling oil is heated to a cracking temperature by circulation over exv ternally fired heating surfaces while taking off vapors including vapors of the desired low boiling product therefrom under superatmospheric pressure, the high boiling oil forming this heated charge is circulated successively through a zone of reduced pressure .and then through a zone of reduced turbulence, the zone of reduced turbulence being maintained in freecommunication with that part ofthe charge circulating over the externally red heating surfaces and under the. first mentioned superatmospheric pressure, vapors are taken oli' from the zone of reduced pressure and pitchy and cokey constituents thereina further concentration of such Vpitchy and cokey constituents as effected within .thezone-of reduced turbulence, and raw high Vboiling oil is supplied to the Charge of oil to maintain the charge as the operation .-proceeds. .The `vapors taken olf -rom the zone offreduced pressure are with advantage are lthus concentrated in the residual oil condensed and such condensate returned to the charge of high boiling oil.

The operation may be carried out without discharge of an residual product from the system durin t e operation. Concentrated pitchy and co ey constituents may, however, be periodically discharged from the zone of reduced turbulence as the operation proceeds to prolong the period of uninterrupted operation.

The invention will be further described in connection with the accompanying drawings which illustrate, diagrammatically and conventionally, in elevation and partly in sectionand with parts broken away, one form of apparatus adapted for carrying out the method of operation of the invention.

The pressure still illustrated in the drawings is of the general type described in -Letters Patent No. 1,285,200 issued to the SinclaircRefining Company November 19, 1918, on my application. This pressure still comprises a bulk supply 'drum 1, a battery of heating tubes 2 arranged in the heating flue of a heating furnace 3, and circulating connections 4, 5 and 6 including a circulating pump 7 for circulating oil from the bulk supply drum through the heating tubes and back to the bulk supply drum. Connection 8 is provided for initially char ing the still at the beginning of a run and or umping out the still at the end ofa run. onnection 9 is provided for supplying cooling'oil to and through the bearings of the circulating pump, as described in Letters Patent No. 1,676,202, issued to the Sinclair Refining Company, July 3, 1928, on the application of myselfY and the late John E. Bell. This pressure still also comprises a settling drum 10 in free communication with the bulk supply drum 1 through connections 11.

The vapors from the bulk supply drum 1 escape through connection 12 to the lower end of reflux tower 13. The condensate from the reflux tower 13, together with any admixed unvaporized stock introduced intothe reflux tower 13, is returned to the pressure still charge through connection 14. The vapors remaining uncondensed escape from the upper end of the reflux tower 13 through connection 15 to condenser 16. This condenser discharges into receiver 17 from which the condensed distillate product is discharged through connection 18, uncondensed vapors and gases being dischar ed through connection 19. Pressure in tie system is maintained and re lated by means of valve 20 between the re ux tower 13 and the condenser 16 or by means of suitable valves arranged beyond the condenser 16 or the receiver 17. Condensation withinthe reflux tower 13 is controlled by the regulated introduction of one or more refluxing media through one or more of the connections 21, 22 and23.

The high boiling oil forming the still charge is circulated, during the operation, through vaporizing drum 24 and settling drum 10, the oil flowing from the bulk supply drum 1 to the vaporizing drum 24 through connection 25 including pressure reducingvalve 26 and the residual oil being forced from vaporizing drum 24 to the settling drum 10 through connections 27 and 28 by means of pump 29 and thence back to the bulk supply drum 1 through connections 11. Connection 30 is provided for pumping out the vaporizing drum 24 or for use in an emergency. Connection 31 is provided for pumping out the settling drum 10 or for periodically discharging conrentrated pitchy and cokey constituents thererom.

Vapors separated in the vaporizing drum 24 escape through connection 32 to the lower end of' reflux tower 33. The condensate from the reflux tower 33 is either discharged or in part discharged through connection 34 or returned or in part returned to the still charge through reflux tower 13 by means of pump 35 and through connection 36 and either connection 37 or connection 21. Vapors remaining uncondensed escape through connection 38 to condenser 39. This condenser discharges into receiver 40 from which condensate is discharged through connection 42. Pressure in the reflux tower 33 and the vaporizing drum 24 may be maintained or regulated by means of valve 43 or by means of suitable valves arranged beyond the condenser or the receiver.

Raw oil is supplied through connection 49 by means of pump 44 and introduced either into the upper end of reflux tower 33 through connection 45 and thence into reflux tower 13 or into the upper end of reflux tower 13 vthrough connection `22. The operation of either or both of the reflux towers 13 and 33 may thus be controlled by the regulated introduction of raw oil. The operation of either or both of these reflux towers may also be controlled, or vcontrol of the operation supplemented, by the regulated introduction of a part of the fraction condensed from the vapors escaping from the tower, through connect-ion 46 by means of pump 47 in the case of ltower 33 and through connection 23 by means of pump 48 in the case of tower 13.

The bulk supply drum 1, the circulating connections 4, 5 and 6, the vaporizing drum 24, the settling drum 10, the connections 25, 27 and 28, vthe reflux towers 13 and 33, and connections 12, 14, 32 and 36 are with advantage lagged or thermally insulated.

Tn carrying out the invention in the apparatus illustrated, pitchy or cokey constituents are with advantage concentrated in the high boiling oil circulating through the vaporizing drum to a maximum permitting maintained circulation of the concentrate through the still system and particularly through the connections between the vaporizing drum and the settling drum 10. This concentration is controlled by controlling the vaporization in the vaporizing drum 24 in turn controlled by regulating the pressure maintained in the vaporizing drum 24 and consequently the pressure differential between the bulk supply drum l and the vaporizing drumA 24, the vaporization in the vaporizing drum 24 being effected by this pressure dii'erent-ial. In carrying out the invention' in the apparatus illustrated for the manufacture of gasoline from gas oil, for example, the pressure in the bulk supply drum may be maintained in the neighborhood of 1001-300 pounds per square inch and the pressure in the vaporizing drum in the neighborhood of 5-5-0 pounds per square inch, the circulating charge of oil in the pressure still system being heated in the heating tubes to a temperature corresponding to the pressure maintained in the bulk supply drum or to a somewhat higher temperature, and the operation of the reflux towers 13 and 33 may be regulated to maintain the temperature of the vapors escaping therefrom in the neighborhood of 37 5-475 F. and

350-425 F. respectively.

Connection 28 communicates with the settling drum 10 through a series of valved connections 51, 52, 53, 54 and 55. These are provided to permit the progressive accumulation of a concentrate of pitchy and cokey constituents in the settling drum 10 as the operation proceeds without interfering with circulation of the high boiling oil forming the pressure still charge through the Vaporizing drum 24 and the settling drum 10 until the drum 10 is lled with such concentrate to a point such that it no longer operates to provide a zone of reduced turbulence. The still is then shut down for cleaning. Or, if this concentrate is being periodically discharged from the settling drum 10, the accumulated concentrate is discharged from the drum 10 somewhat before this point is reached and the operation continued. Such periodic discharge of concentrated pitchy and cokey constituents is limited to a volume such that the consequent lowering of the liquid level in the bulk supply drum 1 does not interfere with circulation of the pressure still charge through the heating tubes. Operating without periodic discharge of concentrated pitchy and cokey constituents, the period of operation is determined, in large measure, by the capacity of the settling drum 10, together with the concentration effected in the vaporizing drum 24.

High boiling oil may be circulated through connection 725, for example, at a rate approximating 40-70% of the rate at which raw oil is supplied through connection 49, where the condensate mixture from the tower 33 is returned to the pressure still through reflux tower 13, and the vaporization in vaporizing drum 24 may be regulated so that the concentrate is formed therein at a rate approximating 515% of the rate\ at which raw oil is supplied through connection 49, the foregoing comparisonsbeing by volume at standard temperature.

I claim:

1. In cracking higher boiling hydrocarbon oils to produce lower boiling hydrocarbon oils, the improvement which comprises heating a charge of high boiling oil to a cracking temperature by circulation over externally fired heating surfaces while taking olf vapors including vapors of the desired low boiling product therefrom under superatmospheric pressure, circulating high boiling oil from said charge through a zone of reduced pressure and then by increasing the pressure on thevoil through a zone of reduced turbulence maintained under the first mentioned superatmospheric pressure and in free communication with the charge circulating over the first mentioned heating surfaces, taking of vapors from said zone of reduced pressure whereby pitchy and cokey constituents are concentrated in the residual oil and effecting a further concentration of such pitchy and cokey constituents in the residual oil within said zone of reduced turbulence, and supplying raw high boiling 'oil to the charge of high boiling oil to maintain the charge as the operation proceeds.

2. In cracking higher boiling hydrocarbon oils to produce lower boiling hydrocarbon oils, the improvement which comprises heating a charge of high boiling oil to a cracking temperature by circulation over externally fired heating surfaces while taking off vapors including vapors of the desired low boiling product therefrom under superatmospheric pressure, circulating high boiling oil from said charge through a zone of reduced pressure and then by increasing the pressure'on the oil through a zone of reduced turbulence maintained under the first mentioned superat-mospheric pressure and in free communication with the charge circulating over the first mentioned heating surfaces, taking off vapors from said zone of reduced pressure whereby' pitchy and cokey constituents are concentrated in the residual oil and effecting a further concentration of such pitchy and cokey constituents in the residual oil within said zone of reduced turbulence, condensing vapors taken off from said zone of reduced pressure and returningI such condensate to the charge of high boiling oil, and supplying raw high boilingoil to the charge of high boiling oil to maintain the charge as the operation proceeds.

3. In cracking high boiling hydrocarbon oils to produce lower boiling hydrocarbon vapors including vapors of the desired low bolling product therefrom under superatmospheric pressure, circulating high boiling oil from said charge through a zone of reduced pressure and then by increasing the pressure on the oil through a zone of reduced turbulence maintained under the first mentioned superatm-ospheric pressure and in free comniunication with the charge circulating over the first mentioned heating surfaces, taking oli" vapors from said zone of' reduced pressure whereby pitchy and coke)7 constituents are concentrated in the residual oil and effecting a further concentration of such pitchy and cokey constituents in the residual oil within said zone of reduced turbulence, periodically discharging concentrated pitchy and cokey constituents from said zone of reduced turbulence las the operation proceeds, and supplying raw high boiling oil to the charge of high boiling oil to maint-ain the charge as the operation proceeds.

In testimony whereof I affix my signature.

EDWARD W. ISOM. 

